Abstract

This specification defines rules and guidelines for adapting the RDFa Core
1.1 and RDFa Lite 1.1 specifications for use in HTML5 and XHTML5. The rules
defined in this specification not only apply to HTML5 documents in non-XML
and XML mode, but also to HTML4 and XHTML documents interpreted through the
HTML5 parsing rules.

Status of This Document

This section describes the status of this document at the time of its publication. Other
documents may supersede this document. A list of current W3C publications and the latest revision
of this technical report can be found in the W3C technical reports
index at http://www.w3.org/TR/.

This document has been reviewed by W3C Members, by software developers,
and by other W3C groups and interested parties, and is endorsed by the
Director as a W3C Recommendation. It is a stable document and may be used
as reference material or cited from another document. W3C's role in making
the Recommendation is to draw attention to the specification and to promote
its widespread deployment. This enhances the functionality and
interoperability of the Web.

This specification is an extension to the HTML5 language. All normative
content in the HTML5 specification, unless specifically overridden by this
specification, is intended to be the basis for this specification.

Note

There are two features in this
specification, @datetime processing and rdf:HTML
literals, that are currently defined as non-normative features. The intent
is that these features will eventually become normative features once the
specification that describes the @datetime attribute [HTML5]
and the specification that defines rdf:HTML [RDF-CONCEPTS]
become W3C Recommendations.
Implementers should implement these features now;
a 2nd (or later) edition of this specification will clarify the long-term
stability of those features. Based on the discussion between the RDFa
Working Group, the HTML Working Group, and the RDF Working Group,
it is not expected that implementation changes will be necessary as
HTML5 and RDF 1.1 advance to Recommendation.

A sample test harness is
available for software developers. This set of tests is not intended to be
exhaustive.
A community-maintained website contains more
information on further reading, developer tools, and software libraries
that can be used to extract and process RDFa data from web documents. The final
implementation report
considered by the Director has been made available to the public.

1. Introduction

This section is non-normative.

Today's web is built predominantly for human readers. Even as
machine-readable data begins to permeate the web, it is typically
distributed in a separate file, with a separate format, and very limited
correspondence between the human and machine versions. As a result, web
browsers can provide only minimal assistance to humans in parsing and
processing web pages: browsers only see presentation information. RDFa is
intended to solve the problem of marking up machine-readable data in HTML
documents. RDFa provides a set of HTML attributes to augment visual data with
machine-readable hints. Using RDFa, authors may turn their existing
human-visible text and links into machine-readable data without repeating
content.

2. Conformance

As well as sections marked as non-normative, all authoring guidelines, diagrams, examples,
and notes in this specification are non-normative. Everything else in this specification is
normative.

The key words MUST, MUST NOT, REQUIRED, SHOULD, SHOULD NOT, RECOMMENDED, MAY,
and OPTIONAL in this specification are to be interpreted as described in [RFC2119].

2.1 Document Conformance

There are two types of document conformance criteria for HTML
documents containing RDFa semantics; HTML+RDFa and
HTML+RDFa Lite.

The following conformance criteria apply to any HTML document
including RDFa markup:

All document conformance requirements stated as mandatory in the
HTML5 specification MUST be met.

The appropriate
Extensions to the HTML5 Syntax,
as described in this document, MUST be considered valid and conforming.
Note that there are fewer supported attributes if the RDFa Lite
syntax [RDFA-LITE] is desired over the more advanced set of RDFa
attributes outlined in RDFa Core.

All HTML5 elements and attributes SHOULD be used in a way that conforms
to [HTML5]. All RDFa attributes SHOULD be used in a way that
is conforms to [RDFA-CORE] and this document.

An example of a conforming HTML+RDFa document, with the RDFa portions
highlighted in green:

Non-XML mode HTML+RDFa 1.1 documents SHOULD be labeled with the Internet
Media Type text/html as defined in
section 12.1
of the HTML5 specification [HTML5].

XML mode XHTML5+RDFa 1.1 documents SHOULD be labeled with the Internet Media
Type application/xhtml+xml as defined in
section 12.3
of the HTML5 specification [HTML5], MUST NOT use a DOCTYPE
declaration for XHTML+RDFa 1.0 or XHTML+RDFa 1.1, and SHOULD NOT use the
@version attribute.

2.2 RDFa Processor Conformance

The RDFa processor conformance criteria are listed below, all of
which are mandatory:

An RDFa processor MUST implement all of the mandatory features
specified in the RDFa Core 1.1 specification [RDFA-CORE].

An RDFa processor MUST support any mandatory features described in this
specification.

2.3 User Agent Conformance

A user agent is considered to be a type of RDFa processor when the
user agent stores or processes RDFa attributes and their values. The
reason there are separate RDFa Processor Conformance and a
User Agent Conformance sections is because one can be a valid
HTML5 RDFa processor but not a valid HTML5 user agent (for example, by only
providing a very small subset of rendering functionality).

The user agent conformance criteria are listed below, all of which are
mandatory:

A user agent MUST implement all of the features required by this
specification.

A user agent MUST implement all of the features required in the RDFa
Core 1.1 specification, excluding those features which are specifically
overridden by this specification as detailed in the Extensions to RDFa Core 1.1.

3. Extensions to RDFa Core 1.1

The RDFa Core 1.1 [RDFA-CORE] specification is the base document on
which this specification builds.
RDFa Core 1.1 specifies the attributes and syntax, in Section 5: Attributes and
Syntax, and processing model, in Section 7: Processing
Model, for extracting RDF from a web document. This section
specifies changes to the attributes and processing model defined in
RDFa Core 1.1 in order to support extracting RDF from HTML documents.

The requirements and rules, as specified in RDFa Core and further
extended in this document, apply to all HTML5 documents. An RDFa processor
operating on both HTML and XHTML documents, specifically on their
resulting DOMs or infosets, MUST apply these processing rules
for HTML4, HTML5 and XHTML5
serializations, DOMs and/or infosets.

3.1 Additional RDFa Processing Rules

Documents conforming to the rules in this specification are processed
according to [RDFA-CORE] with the following extensions:

The default vocabulary URI is undefined.

HTML+RDFa uses an additional initial context by default,
http://www.w3.org/2011/rdfa-context/html-rdfa-1.1, which must
be applied after the initial context for [RDFA-CORE]
(http://www.w3.org/2011/rdfa-context/rdfa-1.1).

The
base can be set
using the base element. For XHTML5+RDFa 1.1 documents,
base can also be set using the @xml:base
attribute.

The
current language
can be set using either the @lang or @xml:lang
attributes. When the @lang attribute and the
@xml:lang attribute are specified on the same element, the
@xml:lang attribute takes precedence. When both
@lang and @xml:lang are specified on the same
element, they MUST have the same value. Further details related to setting the
current language
can be found in section
3.3Specifying the Language for a Literal.

When determining which set of RDFa processing rules to use for documents
served with the application/xhtml+xml media type, a conforming
RDFa processor MUST look at the value in the DOCTYPE declaration of the
document. If a DOCTYPE declaration exists, then the
processing rules are:

XHTML1+RDFa 1.0 for a DOCTYPE of <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML+RDFa 1.0//EN" "http://www.w3.org/MarkUp/DTD/xhtml-rdfa-1.dtd">, or

XHTML1+RDFa 1.1 for a DOCTYPE of <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML+RDFa 1.1//EN" "http://www.w3.org/MarkUp/DTD/xhtml-rdfa-2.dtd">, or

XHTML5+RDFa 1.1 for all other values of DOCTYPE.

Documents served as application/xhtml+xml, that don't contain
a DOCTYPE declaration, and don't specify a @version attribute MUST be interpreted
as XHTML5+RDFa 1.1 documents.

In
Section 7.5:
Sequence, immediately after processing step 4, if the
@property attribute and the @rel and/or
@rev attribute exists on the same element, the non-CURIE and
non-URI @rel and @rev values are ignored. If, after
this, the value of @rel and/or @rev becomes empty,
then the processor MUST act as if the respective attribute is not present.

In
Section 7.5: Sequence, processing step 11, the
HTML5 @datetime attributeMUST be utilized when generating
the current property value, unless @content is also
present on the same element. Otherwise, if @datetime is
present, the current property value must be generated as
follows. The literal value is the value contained in the
@datetime attribute. If @datatype is
present, it is to be used as defined in the RDFa Core [RDFA-CORE]
processing rules. Otherwise, if the value of
@datetime lexically matches a valid
xsd:date, xsd:time, xsd:dateTime,
xsd:duration, xsd:gYear, or
xsd:gYearMonth a typed literal must be generated, with its
datatype set to the matching xsd datatype. Otherwise, a plain literal
MUST be generated, taking into account the
current language.
Implementers should note that the correct order of match testing should be:
xsd:duration, xsd:dateTime,
xsd:date, xsd:time,
xsd:gYearMonth, and xsd:gYear.
This feature is currently non-normative,
see the note on when it will become
normative.

In
Section 7.5: Sequence, processing step 11, if the element is
time, and the element does not have @datetime
or @content attributes, the processor MUST act as if there
is a @datetime attribute containing exactly the elements
text value. This feature is currently non-normative,
see the note on when it will become
normative.

The @version attribute is not supported in HTML5 and is
non-conforming. However, if an HTML+RDFa document contains the
@version attribute on the html element, a conforming
RDFa processor MUST examine the value of this attribute. If the value matches
that of a defined version of RDFa, then the processing rules for that version
MUST be used. If the value does not match a defined version, or there is no
@version attribute, then the processing rules for the most recent
version of RDFa 1.1 MUST be used.

3.2 Modifying the Input Document

RDFa's tree-based processing rules, outlined in
Section 7.5: Sequence of
the RDFa Core 1.1 specification [RDFA-CORE], allow an input document to be
automatically corrected, cleaned-up, re-arranged, or modified in any way that
is approved by the host language prior to processing. Element nesting issues
in HTML documents SHOULD be corrected before the input document is
translated into the DOM, a valid tree-based model, on which the RDFa
processing rules will operate.

Any mechanism that generates a data structure equivalent to the HTML5 or
XHTML5 DOM, such as the html5lib library, MAY be used as the mechanism to
construct the tree-based model provided as input to the RDFa processing
rules.

3.3 Specifying the Language for a Literal

According to RDFa Core 1.1 the
current languageMAY be specified by the host language. In order to conform
to this specification, RDFa processors MUST use the mechanism described in
The lang and xml:lang attributes section of the [HTML5]
specification to determine the
language
of a node.

If the final encapsulating MIME type for an HTML fragment is not decided
on while editing, it is RECOMMENDED that the author
specify both @lang and @xml:lang where the value in
both attributes is exactly the same.

Note

The HTML5 specification takes the
Content-Language HTTP header into account when determining the
language of an element. Some RDFa processor implementations, like those
written in JavaScript, may not have
access to this header and will be non-conforming in the edge case where
the language is only specified in the Content-Language HTTP
header. In these instances, RDFa document authors are urged to
set the language in the document via the @lang
attribute on the html element in order to ensure
that the document is interpreted correctly across all RDFa processors.

3.4 Invalid XMLLiteral Values

When generating literals of type XMLLiteral, the processor MUST ensure
that the output XMLLiteral is a namespace well-formed XML fragment. A
namespace well-formed XML fragment has the following properties:

The XML fragment, when placed inside of a single root element, MUST
validate as well-formed XML. The normative language that describes a
well-formed XML document is specified in Section 2.1 "Well-Formed
XML Documents" of the XML specification.

The XML fragment, when placed inside of a single root element, MUST
retain all active namespace information. The currently active attributes
declared using @xmlns and @xmlns: that are stored in the
RDFa processor's current
evaluation context
in the
IRI mappingsMUST be preserved in the generated XMLLiteral. The PREFIX value for
@xmlns:PREFIXMUST be entirely transformed into lower-case characters
when preserving the value in the XMLLiteral. All active namespaces declared
via @xmlns, @xmlns:, and @prefixMUST be placed in each top-level element in the generated XMLLiteral,
taking care to not overwrite pre-existing namespace values.

An RDFa processor that transforms the XML fragment MUST use the
Coercing an HTML DOM into an infoset algorithm, as specified in the HTML5
specification, followed by the algorithm defined in the Serializing
XHTML Fragments section of the HTML5 specification. If an error or
exception occurs at any point during the transformation, the triple containing
the XMLLiteral MUST NOT be generated.

Transformation to a namespace well-formed XML fragment is required
because an application that consumes XMLLiteral data expects that data to
be a namespace well-formed XML fragment.

The transformation requirement does not apply to plain text input data that are
text-only, such as literals that contain a @datatype attribute
with an empty value (""), or input data that contain only
text nodes.

An example transformation demonstrating the preservation of namespace
values is provided below. The → symbol is used to denote that the line
is a continuation of the previous line and is included purely for the
purposes of readability:

3.5 Property Copying

There are times when authors will find that they have many resources on a
page that share a common set of properties. For example, several
music events may have different performance times, but use
the same location, band, and ticket prices. In this particular case, it is
beneficial to have a short-hand notation to instruct the RDFa processor
to include the location, band, and ticket price information without having
to repeat all of the markup that expresses the data.

HTML+RDFa defines a property copying mechanism which allows
properties associated with a resource to be copied to another resource.
This mechanism can be activated by using the rdfa:copy
predicate.
The feature is illustrated in the following two examples:

In this case, two music events are defined with image,
name, startDate, and location properties. The
image and name values are identical for the two
events and are unnecessarily duplicated in the markup.
Using RDFa's property copying feature, a pattern can be
declared that expresses the common properties. This pattern can then be
copied into other resources within the document:

In this case, the common properties for all of the events are expressed in
the first div. The common properties are copied into each
event resource via the rdfa:copy predicate. The output for the
previous two examples is the same:

In the example above, the properties from #lennon and
#band are copied into the first resource. Then the
properties from #beatles are copied into
#band. Subsequently, those properties are again copied into
the first resource yielding the following output:

Implementers should be aware that a simplistic implementation of
the pattern-copy rule may lead to an infinite loop when
handling circular dependencies. A processor should cease
the pattern-copy rule when no unique triples are generated.

Note

Alternate rules may be used to update the output graph as
long as the end result is the same.

4. Extensions to the HTML5 Syntax

There are a few attributes that are added as extensions to the HTML5
syntax in order to fully support RDFa:

If HTML+RDFa Lite document conformance is desired, all RDFa attributes and
valid values (including CURIEs), as listed in
RDFa Lite 1.1, Section 2: The Attributes,
MUST be allowed and validate as conforming when used in an HTML4, HTML5 or
XHTML5 document. For the avoidance of doubt, the following RDFa attributes
are allowed on all elements in the HTML5 content model: @vocab,
@typeof, @property, @resource, and
@prefix. All other attributes that RDFa may process, such as
@href and @src, are only allowed when consistent
with the content model for that element,
as defined in the HTML5 specification.

If HTML+RDFa document conformance is desired, all RDFa attributes and
valid values (including CURIEs), as listed in
RDFa Core 1.1, Section 2.1: The RDFa Attributes,
MUST be allowed and validate as conforming when used in an HTML4, HTML5 or
XHTML5 document. For the avoidance of doubt, the following RDFa attributes
are allowed on all elements in the HTML5 content model: @vocab,
@typeof, @property, @resource,
@prefix, @content, @about,
@rel, @rev, @datatype, and
@inlist. All other attributes that RDFa may process, such as
@href and @src, are only allowed when consistent
with the content model for that element,
as defined in the HTML5 specification.

If the @property RDFa attribute is present on the
link or meta elements, they MUST be viewed as
conforming if used in the body of the document.
More specifically,
when link or meta elements contain the
RDFa @property attribute and are used in the
body of an HTML5 document, they MUST be considered
flow content.

If the RDFa @property attribute is present on the link
element, the @rel attribute is not required.

If the RDFa @resource attribute is present on the link
element, the @href attribute is not required.

If the RDFa @property attribute is present on the meta
element, neither the @name, @http-equiv, nor @charset attributes are required
and the @content attribute MUST be specified.

5. Backwards Compatibility

RDFa Core 1.1 deprecates the usage of @xmlns: in RDFa 1.1
documents. Web page authors SHOULD NOT use @xmlns: to express
prefix mappings in RDFa 1.1 documents. Web page authors SHOULD use
the @prefix attribute to specify prefix mappings.

However, there are times when XHTML+RDFa 1.0 documents are served by web
servers using the text/html MIME type. In these instances, the
HTML5 specification asserts that the document is processed according to the
non-XML mode HTML5 processing rules. In these particular cases, it is
important that the prefixes declared via @xmlns: are preserved
for the RDFa processors to ensure backwards-compatibility with RDFa 1.0
documents. The following sections elaborate upon the backwards compatibility
requirements for RDFa processor implementations.

5.1 @xmlns:-Prefixed Attributes

The RDFa Core 1.1 [RDFA-CORE] specification deprecates the
use of the @xmlns: mechanism to declare CURIE prefix mappings in
favor of the @prefix attribute. However, there are instances
where its use is unavoidable. For example, publishing legacy documents as HTML5 or
supporting older XHTML+RDFa 1.0 documents that rely on the @xmlns:
attribute.

Since CURIE prefix mappings have been specified using
@xmlns:, and since HTML attribute names are case-insensitive,
CURIE prefix names declared using the @xmlns:attribute-name
pattern xmlns:<PREFIX>="<URI>"SHOULD be specified
using only lower-case characters. For example, the text
"@xmlns:" and the text in "<PREFIX>"SHOULD
be lower-case only. This is to ensure that prefix mappings are interpreted
in the same way between HTML (case-insensitive attribute names) and XHTML
(case-sensitive attribute names) document types.

5.2 Conformance Criteria for @xmlns:-Prefixed Attributes

Since RDFa 1.0 documents may contain attributes starting with
@xmlns: to specify CURIE prefixes, any attribute starting with
a case-insensitive match on the text string "@xmlns:" MUST be
preserved in the DOM or other tree-like model that is passed to the RDFa
Processor.
For documents conforming to this specification, attributes with
names that have a case insensitive prefix matching "@xmlns:"
MUST be considered conforming. Conformance checkers SHOULD
accept attribute names that have a case insensitive prefix matching
"@xmlns:" as conforming. Conformance checkers SHOULD generate
warnings noting that the use of @xmlns: is deprecated.
Conformance checkers MAY report the use of xmlns: as an error.

All attributes starting with a case insensitive prefix matching
"@xmlns:" MUST conform to the production rules outlined in
Namespaces in XML [XML-NAMES11],
Section 3: Declaring Namespaces.
Documents that contain @xmlns: attributes that do not conform to
Namespaces in XML MUST NOT be accepted as conforming.

5.3 Preserving Namespaces via Coercion to Infoset

RDFa 1.0 documents may contain the @xmlns: pattern to
declare prefix mappings, it is important that namespace information that
is declared in non-XML mode HTML5 documents are mapped to an infoset
correctly. In order to ensure this mapping is performed correctly, the
"Coercing an HTML DOM into an infoset" rules defined in [HTML5]
must be extended to include the following rule:

If the XML API is namespace-aware, the tool must ensure that
([namespace
name], [local name],
[normalized
value]) namespace tuples are created when converting the non-XML mode
DOM into an infoset. Given a standard @xmlns: definition,
xmlns:foo="http://example.org/bar#", the [namespace name]
is http://www.w3.org/2000/xmlns/,
the [local name] is foo, and the
[normalized value] is http://example.org/bar#, thus the
namespace tuple would be (http://www.w3.org/2000/xmlns/,
foo, http://example.org/bar#).

For example, given the following input text:

Example 12

<div xmlns:com="https://w3id.org/commerce#">

The div element above, when coerced from an HTML DOM into
an infoset, should contain an attribute in the [namespace
attributes] list with a [namespace name] set to
"http://www.w3.org/2000/xmlns/", a [local name] set to
com, and a [normalized value] of
"https://w3id.org/commerce#".

5.4 Infoset-based Processors

While the intent of the RDFa processing instructions is to provide a
set of rules that are as language and toolchain independent as possible, for
the sake of clarity, detailed methods of extracting RDFa content from
processors operating on an XML Information Set are provided below.

5.4.1 Extracting URI Mappings from Infosets

Extracting URI Mappings declared via @xmlns:
while operating from within an infoset-based RDFa processor can be achieved
using the following algorithm:

For each attribute in the [attributes] list
that has no value for [prefix] and a
[local
name] that starts with @xmlns:, create an [IRI mapping] by
storing the [local name] part with the @xmlns: characters
removed as the value to be mapped, and the [normalized
value] as the value to map.

Note

This step is unnecessary if the infoset coercion
rules preserve namespaces specified in non-XML mode.

For example, assume that the following markup is processed by an
infoset-based RDFa processor:

Example 13

<div xmlns:ps="https://w3id.org/payswarm#" ...

After the markup is processed, there should exist a [URI mapping] in
the [local list of URI mappings] that contains a mapping from
ps to https://w3id.org/payswarm#.

5.4.2 Processing RDFa Attributes

There are a number of non-prefixed attributes that are associated with
RDFa Processing in HTML5. If an XML Information Set based RDFa processor is
used to process these attributes, the following algorithm should be used to
detect and extract the values of the attributes.

For each Attribute Information Item specific to RDFa in the infoset
[attributes]
list that has a [prefix] with
no value, extract and use the [normalized
value].

5.5 DOM Level 1 and Level 2-based Processors

Most DOM-aware RDFa processors are capable of accessing DOM Level 1
[DOM-LEVEL-1]
methods to process attributes on elements. To discover all
@xmlns:-specified CURIE prefix mappings, the
Node.attributes
NamedNodeMap can be iterated over. Each
Attr.name that
starts with the text string @xmlns: specifies a CURIE prefix
mapping. The value to be mapped is the string after the @xmlns:
substring in the Attr.name variable and the value to be mapped is
the value of the Attr.value variable.

The intent of the RDFa processing instructions are to provide a
set of rules that are as language and toolchain independent as possible. If
a developer chooses to not use the DOM1 environment mechanism outlined in
the previous paragraph, they may use the following DOM2 [DOM-LEVEL-2-CORE]
environment mechanism.

5.5.1 Extracting URI Mappings via DOM Level 2

Extracting URI Mappings declared via @xmlns: while operating
from within a DOM Level 2 based RDFa processor can be achieved using the
following algorithm:

This step is unnecessary if the XML and non-XML
mode DOMs are namespace consistent.

For example, assume that the following markup is processed by a
DOM2-based RDFa processor:

Example 14

<div xmlns:com="https://w3id.org/commerce#" ...

After the markup is processed, there should exist a [URI mapping] in
the [local list of URI mappings] that contains a mapping from
com to https://w3id.org/commerce#.

5.5.2 Processing RDFa Attributes

There are a number of non-prefixed attributes that are associated with
RDFa processing in HTML5. If an DOM2-based RDFa processor is used to
process these attributes, the following algorithm should be used to detect
and extract the values of the attributes.

When extracting values from @href and
@src, web authors and developers should
note that certain values MAY be transformed if accessed via the DOM versus
a non-DOM processor. The rules for modification of URL values can be
found in the main HTML5 specification under
Section 2.5: URLs.

A. About this Document

A.1 History

This section is non-normative.

In early 2004, Mark Birbeck published a document named "RDF in XHTML"
via the XHTML2 Working Group wherein he laid
the groundwork for what would eventually become RDFa (The Resource
Description Framework in Attributes).

In 2006, the work was co-sponsored by the Semantic Web Deployment Working
Group, which began to formalize a technology to express semantic data in
XHTML. This technology was successfully developed and reached consensus at
the W3C, later published as an official W3C Recommendation. While HTML
provides a mechanism to express the structure of a document (title,
paragraphs, links), RDFa provides a mechanism to express the meaning in a
document (people, places, events).

The document, titled "RDF in XHTML: Syntax and Processing" [XHTML-RDFA],
defined a set of attributes and rules for
processing those attributes that resulted in the output of machine-readable
semantic data. While the document applied to XHTML, the attributes and
rules were always intended to operate across any tree-based structure
containing attributes on tree nodes (such as HTML4, SVG and ODF).

While RDFa was initially specified for use in XHTML, adoption by a
number of large organizations on the web spurred RDFa's use in non-XHTML
languages. Its use in HTML4, before an official specification was developed
for those languages, caused concern regarding document conformance.

Over the years, the members of the
RDFa Community had discussed the possibility
of applying
the same attributes and processing rules outlined in the XHTML+RDFa
specification to all HTML family documents. By design, the possibility of a
unified semantic data expression mechanism between all HTML and XHTML
family documents was squarely in the realm of possibility.

An RDFa Working Group was created in 2010 to address the issues concerning
multiple language implementations of RDFa. The XHTML+RDFa document was split
into a base specification, called RDFa Core 1.1 [RDFA-CORE], and thin
specifications that layer above RDFa Core 1.1. The XHTML+RDFa 1.1 specification
[XHTML-RDFA] is an example of such a thin specification. This
document, also a thin specification, is targeted at HTML4, HTML5 and
XHTML5.

This document describes the extensions to the RDFa Core 1.1
specification that permits the use of RDFa in all HTML family documents. By
using the attributes and processing rules described in the RDFa Core 1.1
specification and heeding the minor changes in this document, authors can
generate markup that produces the same semantic data output in
HTML4, HTML5 and XHTML5.

2011-12-30: Addition of normative dependency for RDFa Lite 1.1.
Addition of rules to allow meta and
link elements in flow and phrasing content as long as they
contain at least one RDFa-specific attribute. Added support for
@datetime and value processing.

2012-03-10: Clarification of where each RDFa attribute is allowed to be
used. Feature at risk warning for HTML4+RDFa DTD-based validation.

2012-09-10: Publishing control of the HTML+RDFa document is handed over
from the HTML WG to the newly re-chartered RDFa WG. DTD-based validation is
removed from the specification.

2012-12-13: Addition of new HTML-specific processing rules for dealing with
XHTML5 vs. HTML5 documents, xml:base, HTML Literals, property and rel/rev on
the same element, and more types for the datetime attribute.

2012-12-27: Added Property Copying section and special processing for
head and body.